Bearing device

ABSTRACT

A bearing device includes: a journal part, a main bearing, a cylinder block, and a bearing cap. One half bearing held by the cylinder block includes: a first circumferential oil groove and a second circumferential oil groove being formed at positions opposite to an inlet of an oil passage of the journal part; a separation part separating the first circumferential oil groove and the second circumferential oil groove; and a first oil hole and a second oil hole respectively penetrating from the first circumferential oil groove and the second circumferential oil groove to an outer circumferential surface. The cylinder block includes an oil distribution passage which is formed so as to extend across both the first oil hole and the second oil hole of the one half bearing.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a bearing device of a crankshaft, andmore particularly to a bearing device which includes a journal part of acrankshaft, a main bearing which rotatably supports the journal part,and a cylinder block and a bearing cap which hold the main bearing.

(2) Description of Related Art

A crankshaft of an internal combustion engine is supported at itsjournal part, through a main bearing constituted of a pair of halfbearings, under a cylinder block of the internal combustion engine. Tolubricate this main bearing, lubricating oil discharged by an oil pumpis fed through an oil gallery formed inside a wall of the cylinder blockand a through-hole formed in a wall of the main bearing, into alubricating oil groove which is formed along an inner circumferentialsurface of the main bearing. The crankshaft is formed with a firstlubricating oil passage penetrating the journal part in the diametricaldirection, and the first lubricating oil passage communicates throughopenings at its both ends with a circumferential oil groove of the mainbearing. A second lubricating oil passage branching off from the firstlubricating oil passage is formed so as to pass through a crankarm part,and the second lubricating oil passage communicates with a thirdlubricating oil passage formed to penetrate a crankpin in thediametrical direction. Thus, the lubricating oil fed into thelubricating oil groove of the main bearing passes through the firstlubricating oil passage, the second lubricating oil passage, and thethird lubricating oil passage, and thereafter is fed through an opening(a lubricating oil outlet formed in an outer circumferential surface ofthe crankpin) at an end part of the third lubricating oil passage, ontosliding surface between the crankpin and a connecting rod bearing.

In recent years, the oil pump for supplying lubricating oil has beenreduced in size with the aim of lowering the fuel consumption of theinternal combustion engine. In response to this trend, a main bearinghas been proposed, wherein at least one of the pair of half bearingsconstituting the main bearing includes: an oil hole for introducinglubricating oil which penetrates a bearing wall plate; an oildistribution groove which extends in a circumferential direction in aninner circumferential surface and communicates with the oil hole; and acollection groove which extends in the circumferential direction tocollect the lubricating oil on the inner circumferential surface of thehalf bearing without communicating with the oil distribution groove(e.g., see FIG. 2 of International Publication No. WO 2012/123213).

In this main bearing of International Publication No. WO 2012/123213,since the lubricating oil supplied from the oil gallery inside thecylinder block to the main bearing flows only into the oil distributiongroove and does not flow into the collection groove, the amount of oilsupplied to the main bearing can be reduced. That is, making the oilflow to the connecting rod bearing through the first lubricating oilpassage, the second lubricating oil passage, and the third lubricatingoil passage requires the lubricating oil inside the oil distributiongroove to be at a high pressure. The flow rate of the lubricating oil tobe supplied can be lowered by reducing the volume of the oildistribution groove as is shown in International Publication No. WO2012/123213.

A negative pressure is generated in the collection groove of the mainbearing of International Publication No. WO 2012/123213, since thecollection groove is a closed space without the oil hole whichpenetrates the bearing wall plate to introduce the lubricating oil.

This creates a suctioning effect due to the negative pressure, whichcauses the surrounding lubricating oil to be suctioned. As the suctionedlubricating oil is again supplied onto the inner circumferentialsurface, the amount of lubricating oil supplied to the main bearing canbe reduced. International Publication No. WO 2012/123213 achieves thereduction in size of the oil pump by means of the effect describedabove.

BRIEF SUMMARY OF THE INVENTION

There is a problem in the bearing device of the crankshaft using themain bearing of International Publication No. WO 2012/123213: that is,during operation of the internal combustion engine, the lubricating oilis sufficiently supplied to the crankpin part (to a clearance betweenthe crankpin surface and the inner circumferential surface of thecrankpin part bearing) as long as an inlet of the first lubricating oilpassage of the journal part is in communication with the oildistribution groove of the half bearing. However, the lubricating oilsupply to the crankpin part becomes insufficient and the crankpin partbearing is likely to be damaged while the inlet of the first lubricatingoil passage is in communication with the collection groove.

In addition, by the end of communication between the inlet of the firstlubricating oil passage and the collection groove, the amount of oilinside the collection groove has become small. Thus, immediately afterthe termination of the communication, the amount of the lubricating oilon the inner circumferential surface becomes insufficient near thecollection groove, and damage is likely to occur as the innercircumferential surface of the half bearing comes into direct contactwith the journal surface.

In view of this, it is an object of the present invention to provide abearing device which not only can reduce the amount of lubricating oilsupplied to the main bearing, but also is excellent in supplying thelubricating oil to the crankpin part.

To achieve the above object, the present invention provides a bearingdevice for rotatably supporting a journal part of a crankshaft. Thebearing device includes: a journal part having an oil passage extendinginside thereof and an inlet of the oil passage being open on an outercircumferential surface of the journal part; a main bearing beingconstituted of a pair of half bearings and rotatably supporting thejournal part; and a cylinder block and a bearing cap being each formedwith a holding bore for holding the main bearing. One half bearing beingheld in the holding bore of the cylinder block includes: a firstcircumferential oil groove and a second circumferential oil groove beingformed at positions opposite to the inlet of the oil passage of thejournal part in an inner circumferential surface of the one halfbearing; a separation part separating the first circumferential oilgroove and the second circumferential oil groove; and a first oil holeand a second oil hole respectively penetrating from the firstcircumferential oil groove and the second circumferential oil groove toan outer circumferential surface of the one half bearing. The cylinderblock has an oil distribution passage, which is formed so as to extendacross both the first oil hole and the second oil hole of the one halfbearing, in a holding surface constituting the holding bore.

Here, the crankshaft refers to a member which includes a journal part, acrankpin part, and a crankarm part. The half bearing refers to a memberhaving a shape of a ring divided substantially into halves, which,however, are not necessarily halves in the strict sense.

Thus, the bearing device of the present invention is characterized inthat one of the half bearings which is held in the holding bore of thecylinder block has the first circumferential oil groove and the secondcircumferential oil groove, the separation part, and the first oil holeand the second oil hole, and that the cylinder block has the oildistribution passage which is formed so as to extend across both thefirst oil hole and the second oil hole.

According to this configuration, a part of the lubricating oil issupplied to the second circumferential oil groove through the oildistribution passage and the second oil hole even when the inlet of theoil passage of the journal part is in communication with the firstcircumferential oil groove. For this reason, it is unlikely that theamount of the lubricating oil on the inner circumferential surfacebecomes insufficient near the second circumferential oil groove and theinner circumferential surface of the half bearing comes into directcontact with the surface of the journal part.

Moreover, a large part of the lubricating oil is fed alternately to thefirst circumferential oil groove and the second circumferential oilgroove. Thus, since the amount of oil discharged by the oil pump can beset on the basis of the internal volume of one circumferential oilgroove, a sufficient amount of lubricating oil can be supplied even by asmall oil pump. In addition, since the lubricating oil is supplied tothe oil passage of the journal part through both the circumferential oilgrooves, the lubricating oil can be continuously supplied to thecrankpin part.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a cross-sectional view of a crankshaft of an internalcombustion engine cut at a journal part and a crankpin part;

FIG. 2 is a cross-sectional view illustrating a configuration of abearing device of Embodiment 1;

FIG. 3 is a side view illustrating a configuration of a half bearing ofEmbodiment 1;

FIG. 4 is a bottom view illustrating the configuration of the halfbearing of Embodiment 1;

FIG. 5A is a view illustrating the operation of the bearing device ofEmbodiment 1 in a state where an inlet of an oil passage is incommunication with a first circumferential oil groove;

FIG. 5B is a view illustrating the operation of the bearing device ofEmbodiment 1 in a state where the inlet of the oil passage is incommunication with a second circumferential oil groove;

FIG. 6 is an enlarged view illustrating the operation of the bearingdevice of Embodiment 1;

FIG. 7 is a side view illustrating a configuration of a half bearing ofEmbodiment 2;

FIG. 8 is a side view illustrating a configuration of a half bearing ofEmbodiment 3;

FIG. 9 is a side view illustrating a configuration of a half bearing ofEmbodiment 4;

FIG. 10 is an internal view illustrating the configuration of the halfbearing of Embodiment 4;

FIG. 11 is a cross-sectional view illustrating a cross-sectional shapeof the circumferential groove of Embodiment 1;

FIG. 12 is a cross-sectional view illustrating a cross-sectional shapeof a circumferential groove of another form;

FIG. 13 is a cross-sectional view illustrating a cross-sectional shapeof a circumferential groove of another form;

FIG. 14 is a view illustrating a length L2 of the inlet;

FIG. 15 is a bottom view illustrating an arrangement of a first oil holeand a second oil hole of another form; and

FIG. 16 is a cross-sectional view illustrating a configuration of aconventional bearing device.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of the present invention will be describedwith reference to the drawings.

Embodiment 1 (Overall Configuration of the Bearing Device)

First, an overall configuration of a bearing device 1 of this embodimentwill be described with reference to FIGS. 1 and 2. As shown in FIG. 1,the bearing device 1 of this embodiment includes: a journal part 6having a first lubricating oil passage 6 a as an oil passage extendinginside the journal part 6 and inlets 6 b, 6 b of the first lubricatingoil passage 6 a being open on an outer circumferential surface of thejournal part 6; a main bearing 4 being constituted of a pair of halfbearings 41 and 42 and rotatably supporting the journal part 6; and acylinder block 81 and a bearing cap 82 being formed with holding bores81 a and 82 a respectively for holding the main bearing 4.

In addition to the above, the bearing device 1 includes: a crankpin part5 which is formed integrally with the journal part 6 through a crankarmpart (not shown) and rotates around the journal part 6; a connecting rod2 which transmits reciprocating movement from an internal combustionengine to the crankpin part 5; and a connecting rod bearing 3 whichrotatably supports the connecting rod 2.

Although the crankshaft in practice includes multiple journal parts 6and multiple crankpin parts 5, only one journal part 6 and one crankpinpart 5 are shown here for the convenience of illustration. In FIG. 1,the positional relationship in a depth direction of the drawing is thatthe journal part 6 is on the farther side in the drawing and thecrankpin part 5 is on the nearer side.

(Configuration of the Journal Part)

The journal part 6 serves as a rotary shaft when the crankshaft rotates,and is formed of metal in a short columnar shape integral with thecrankarm part (not shown) and the crankpin part 5. The journal part 6 isrotatably supported under the cylinder block 81 of the internalcombustion engine through the main bearing 4 constituted of the pair ofhalf bearings 41 and 42. The journal part 6 includes the firstlubricating oil passage 6 a as an oil passage extending inside thereof,and the inlets 6 b, 6 b which is open on the outer circumferentialsurface of the journal part 6 at both ends of the first lubricating oilpassage 6 a. A second lubricating oil passage 5 a is formed whichbranches off from the first lubricating oil passage 6 a and passesthrough the crankarm part, and the second lubricating oil passage 5 acommunicates with a third lubricating oil passage 5 b extending insidethe crankpin part 5.

The first lubricating oil passage 6 a of the journal part 6 extendslinearly to penetrate the columnar shape of the journal part 6 at itsmaximum diameter part in the diametrical direction, forming the twoinlets 6 b, 6 b in the surface of the journal part 6. As the two inlets6 b, 6 b are separated from each other at an angle of 180° in thecircumferential direction of the journal part 6, the inlets 6 b, 6 balternately communicate with the first circumferential oil groove 41 aand the second circumferential oil groove 41 b.

Unlike this embodiment, if an oil passage is formed, for example, in anL-shape with the two inlets of the journal part forming acircumferential angle of 90° (270°) around the central axis of thejournal part, a state periodically occurs in which the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b communicate simultaneously with the inlets. This makes itnecessary to set the discharge flow rate of the oil pump on the basis ofan internal volume obtained by adding up the internal volumes of thefirst circumferential oil groove 41 a and the second circumferential oilgroove 41 b. Thus, the reduction in size of the oil pump cannot beachieved. Moreover, in this case, a state periodically occurs in whichthe first circumferential oil groove 41 a and the second circumferentialoil groove 41 b do not communicate with either of the inlets, duringwhich the lubricating oil is not supplied to the connecting rod bearing3.

As shown in FIGS. 5A and 5B, the inlet 6 b has a circular shape with thesame area as a cross-sectional area of the first lubricating oil passage6 a viewed in the axial direction. However, the present invention is notlimited to this example. The inlet 6 b may have a larger area than thefirst lubricating oil passage 6 a as shown in FIG. 14, or may have anoval shape in the outer circumferential surface of the journal part 6.When the area of the inlet 6 b is larger than the cross-sectional areaof the first lubricating oil passage 6 a, a transition part 6 c, whichgradually changes (decreases) in cross-sectional area along the axialdirection of the first lubricating oil passage 6 a, is formed with adepth of 1 to 2 mm between the inlet 6 b and the first lubricatingpassage 6 a.

(Configuration of the Half Bearing)

As shown in FIGS. 2 to 4, the main bearing 4 is constituted of acombination of the two half bearings 41 and 42 butted against each otherat their end surfaces into a cylindrical shape. The upper half bearing41 is fitted into the holding bore 81 a of the cylinder block 81, whilethe lower half bearing 42 is fitted into the holding bore 82 a of thebearing cap 82, and as a whole, the half bearings 41 and 42 form acylindrical shape.

In the following, the upper half bearing 41 of the two half bearings 41and 42 will be described, which has a shape characteristic of thepresent invention. It is preferable that the lower half bearing 42 has ageneral shape, and does not have the first circumferential oil groove,the second circumferential oil groove, the first oil hole, and thesecond oil hole, which will be described later. This is because when thelower half bearing 42 is provided with the circumferential oil groove,the required supply of lubricating oil increases by the amountcorresponding to the internal volume of the circumferential oil groove,making it difficult to achieve the reduction in size of the oil pump.

As shown in FIG. 3, the upper half bearing 41 is formed of bimetalobtained by laminating a bearing alloy onto a steel plate into asemi-cylindrical shape. The half bearing 41 includes: a firstcircumferential oil groove 41 a and a second circumferential oil groove41 b which are formed at positions opposite to the inlet 6 b of thefirst lubricating oil passage 6 a of the journal part 6 in the innercircumferential surface of the one half bearing 41; a separation part 41c which separates the first circumferential oil groove 41 a and thesecond circumferential oil groove 41 b; and a first oil hole 41 d and asecond oil hole 41 e which respectively penetrate from the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b to the outer circumferential surface of the one half bearing41. The half bearing 41 has a symmetrical shape with respect to theseparation part 41 c in the center.

As can be seen from FIGS. 2 and 3, the first circumferential oil groove41 a and the second circumferential oil groove 41 b formed in the innercircumferential surface of the half bearing 41 extend fromcircumferential end surfaces 41 g, 41 g of the half bearing 41 towardthe center in the circumferential direction. The first circumferentialoil groove 41 a and the second circumferential oil groove 41 b are eachformed with a constant depth in a region except for near the center, andformed so as to gradually decrease in depth toward the separation part41 c near the center.

The first circumferential oil groove 41 a and the second circumferentialoil groove 41 b do not extend up to the center in the circumferentialdirection of the half bearing 41, and therefore an inner circumferentialsurface 41 f partially remains between the end part of the firstcircumferential oil groove 41 a on the center side and the end part ofthe second circumferential oil groove 41 b on the center side (FIGS. 2,3, and 4). Hereinafter, the part of the inner circumferential surfacepartially remaining over the length L1 so as to separate (partition) thefirst circumferential oil groove 41 a and the second circumferential oilgroove 41 b is referred to as the separation part 41 c (the shadedportion in FIG. 4). In other words, the first circumferential oil groove41 a and the second circumferential oil groove 41 b extend over theentire length in the circumferential direction except for the length ofthe separation part 41 c in the center. The length L1 in thecircumferential direction of the separation part 41 c is defined as alength measured along the cylindrical surface which forms the innercircumferential surface 41 f.

As shown in FIG. 11, the cross-sections of the first circumferential oilgroove 41 a and the second circumferential oil groove 41 b are formed ina rectangular shape. However, the cross-section may have a semi-circularshape or a round shape as shown in FIG. 12, or an inverted trapezoidalshape (a trapezoidal shape wider at the inner circumferential side) asshown in FIG. 13.

As can be seen from FIG. 4, the first circumferential oil groove 41 aand the second circumferential oil groove 41 b are positioned at themiddle of the width in the axial direction of the half bearing 41. Thebottom parts (deepest parts) of the first circumferential oil groove 41a and the second circumferential oil groove 41 b are formed respectivelywith the first oil hole 41 d and the second oil hole 41 e whichpenetrate the wall plate of the half bearing 41 in the radial direction.Thus, the lubricating oil flows from the oil gallery 81 c inside thewall of the cylinder block 81 to the oil distribution passage 81 b ofthe holding bore 81 a in the cylinder block 81, and thereafter issupplied through the first oil hole 41 d and the second oil hole 41 e tothe first circumferential oil groove 41 a and the second circumferentialoil groove 41 b, respectively.

The first circumferential oil groove 41 a and the second circumferentialoil groove 41 b are formed so that their positions at the middle in thewidth direction match the center position of the inlet 6 b of the firstlubricating oil passage 6 a of the journal part 6 (in FIG. 4, the inlet6 b at a rotation position shown in FIG. 6 is indicated by a broken lineand overlapped with the separation part 41 c). This allows thelubricating oil supplied to the first circumferential oil groove 41 aand the second circumferential oil groove 41 b to flow easily throughthe inlet 6 b (see FIG. 2) to the connecting rod bearing 3.

It is preferable that the first circumferential oil groove 41 a and thesecond circumferential oil groove 41 b are formed so that they cover aposition at least at an circumferential angle of 45° (135°) from thecircumferential end surface 41 g of the half bearing 41, and extendtoward the center when viewed in the circumferential direction. Thereason is as follows.

In principle, a centrifugal force acts on the lubricating oil inside thefirst lubricating oil passage 6 a of the rotating journal part 6, whichcreates resistance when the lubricating oil inside the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b flows from the inlet 6 b into the inside of the firstlubricating oil passage 6 a. In a region nearer to the center in thecircumferential direction from the position of a circumferential angleof 45° (135°) from the circumferential end surface 41 g of the halfbearing 41, however, the direction of gravity acting on the lubricatingoil becomes opposite to the direction in which the centrifugal forceacts (the direction of the gravity becomes more directly opposite to thedirection of the centrifugal force at a position closer to the center),so that the gravity counteracts the centrifugal force. This allows thelubricating oil inside the first circumferential oil groove 41 a and thesecond circumferential oil groove 41 b to flow more easily in theabove-mentioned region into the inlet 6 b of the first lubricating oilpassage 6 a of the journal part 6.

It is preferable that the first oil hole 41 d and the second oil hole 41e are formed at a position other than near the end part of the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b on the center side in the circumferential direction of thehalf bearing 41. The reason is as follows.

For example, if the oil hole is formed at the end part of thecircumferential oil groove, which is on the front side in a rotationaldirection X of the journal part 6 of the half bearing 41 (in FIG. 6, thecircumferential oil groove 41 b on the right side), on the center sidein the circumferential direction of the half bearing 41, where thegroove depth is formed to be small, a large part of the lubricating oilflowing from the oil hole directly flows into the first lubricating oilpassage 6 a of the journal part 6 when the inlet 6 b of the firstlubricating oil passage 6 a of the journal part 6 passes this oil holeposition. Accordingly, it takes time before the entire circumferentialoil groove 41 b is filled with the lubricating oil. Especially duringhigh-speed rotation of the crankshaft, the inlet 6 b of the journal part6 moves toward the leading side in the circumferential direction at ahigh speed, so that filling of the circumferential oil groove 41 b withthe lubricating oil cannot follow. For this reason, it is likely thatsupply of the lubricating oil to the connecting rod bearing 3 becomesinsufficient.

In this embodiment, it is preferable that the length L1 in thecircumferential direction of the separation part 41 c at the position inthe inner circumferential surface 41 f of the half bearing 41 and thelength L2 in the circumferential direction of the inlet 6 b of the firstlubricating oil passage 6 a of the journal part 6 satisfy the followingrelational expression. That is, it is preferable that the length L1 inthe circumferential direction of the separation part 41 c at theposition in the inner circumferential surface 41 f of the half bearing41 is smaller than the length L2 in the circumferential direction of theinlet 6 b of the journal part 6. Moreover, it is preferable that theexpression L1≧L2×0.5 is satisfied. In addition, it is preferable thatthe expression L2-L1>0.5 (mm) is satisfied.

While the dimension of the inlet 6 b of the lubricating oil passage 6 ainside the journal part 6 differs according to the specifications of theinternal combustion engine, the diameter is, for example, approximately5 to 8 mm in the case of a small internal combustion engine of passengercars. Similarly, in the case of a small internal combustion engine, thegroove width of the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b is approximately 3 to 6 mm, and thegroove depth (except for the region at the circumferential end partwhere the groove depth is small) is approximately 0.5 to 1.5 mm.

Moreover, it is preferable that the length L1 in the circumferentialdirection of the separation part 41 c is 1 mm or longer.

(Configuration of the Cylinder Block)

The cylinder block 81 includes: the holding bore 81 a which holds theupper half bearing 41; the oil distribution passage 81 b which is formedin the holding surface constituting the holding bore 81 a so as toextend across both the first oil hole 41 d and the second oil hole 41 eof the upper half bearing 41; and the oil gallery 81 c which suppliesthe lubricating oil discharged from the oil pump to the oil distributionpassage 81 b.

It is preferable that the oil distribution passage 81 b is formed on thecylinder block 81 side instead of on the half bearing 41 side. This isbecause forming the oil distribution passage 81 b in the holding surfaceof the holding bore 81 a of the cylinder block 81 allows the internalvolume of the oil distribution passage 81 b to be set to a largervolume. In contrast, when the groove serving as the oil distributionpassage is formed in the back surface (outer circumferential surface) ofthe half bearing so as to connect the first oil hole and the second oilhole, it is difficult to secure a sufficient volume as the oildistribution passage due to the limited wall thickness of the halfbearing.

It is preferable that the total internal volume obtained by adding upthe internal volume of the first circumferential oil groove 41 a and theinternal volume of the second circumferential oil groove 41 b of thehalf bearing 41 is smaller than the internal volume of the oildistribution passage 81 b of the cylinder block 81. The reason is asfollows.

The first circumferential oil groove 41 a and the second circumferentialoil groove 41 b can communicate with each other through the inlet 6 b ofthe first lubricating oil passage 6 a of the journal part 6, since thelength L1 in the circumferential direction of the separation part 41 cis smaller than the length L2 in the circumferential direction of theinlet 6 b of the journal part 6. Therefore, as shown in FIG. 6, at themoment the inlet 6 b terminates the communication with one of thegrooves, i.e. the first circumferential oil groove 41 a, and startscommunication with the other groove, i.e. the second circumferential oilgroove 41 b, the lubricating oil inside the oil distribution passage 81b flows to both the circumferential oil grooves 41 a and 41 b. As aresult, the amount of the lubricating oil inside the circumferential oilgrooves 41 a and 41 b can become insufficient.

If “the internal volume of the first circumferential oil groove 41 a+theinternal volume of the second circumferential oil groove 41 b<theinternal volume of the oil distribution passage 81 b”, the amount oflubricating oil which is instantaneously required can be secured insidethe oil distribution passage 81 b, so that the situation where theamount of the lubricating oil supplied to the circumferential oilgrooves 41 a and 41 b becomes instantaneously insufficient can beprevented.

(Operation)

Next, the operation of the bearing device 1 of this embodiment will bedescribed. During operation of the internal combustion engine, thelubricating oil discharged from the oil pump flows through the oilgallery 81 c of the cylinder block 81, the oil distribution passage 81 bof the cylinder block 81, the first oil hole 41 d and the second oilhole 41 e, and the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b, in this order.

One part of the lubricating oil inside the first and secondcircumferential oil grooves 41 a and 41 b flows onto the innercircumferential surface of the half bearing 41 (to the clearance betweenthe inner circumferential surface of the half bearing 41 and the outercircumferential surface of the journal part 6), and another part of thelubricating oil flows into the first lubricating oil passage 6 a fromthe inlet 6 b of the journal part 6. The lubricating oil having flowedinto the first lubricating oil passage 6 a is further fed to thecrankpin part 5 through the second lubricating oil passage 5 a and thethird lubricating oil passage 5 b.

As shown in FIG. 5A, while the inlet 6 b of the first lubricating oilpassage 6 a of the journal part 6 of the crankshaft is in communicationwith the first circumferential oil groove 41 a of the half bearing 41, alarge part of the lubricating oil inside the oil distribution passage 81b of the cylinder block 81 flows through the first oil hole 41 d of thehalf bearing 41 to the first circumferential oil groove 41 a, and only apart of the lubricating oil flows through the second oil hole 41 e tothe second circumferential oil groove 41 b.

As shown in FIG. 5B, while the inlet 6 b of the first lubricating oilpassage 6 a of the journal part 6 of the crankshaft is in communicationwith the second circumferential oil groove 41 b of the half bearing 41,a large part of the lubricating oil inside the oil distribution passage81 b of the cylinder block 81 flows through the second oil hole 41 e ofthe half bearing 41 to the second circumferential oil groove 41 b, andonly a part of the lubricating oil flows through the first oil hole 41 dto the first circumferential oil groove 41 a.

Thus, in the bearing device 1 of this embodiment, a large part of thelubricating oil is alternately fed to the first circumferential oilgroove 41 a and the second circumferential oil groove 41 b. That is, thedischarge flow rate of the oil pump can be set on the basis of theinternal volume of only one circumferential oil groove 41 a (41 b).Therefore, the required oil amount can be supplied even by a small oilpump.

The inlet 6 b of the first lubricating oil passage 6 a of the journalpart 6 is always in communication with at least one of the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b. Thus, the lubricating oil can be continuously supplied tothe crankpin part 5.

As shown in FIG. 5A, while the inlet 6 b of the first lubricating oilpassage 6 a of the journal part 6 of the crankshaft is in communicationwith the first circumferential oil groove 41 a, a part of thelubricating oil inside the oil distribution passage 81 b of the cylinderblock 81 flows to the second circumferential oil groove 41 b through thesecond oil hole 41 e of the half bearing 41. For this reason, it isunlikely that the amount of the lubricating oil on the innercircumferential surface 41 f surrounding the second circumferential oilgroove 41 b becomes insufficient and thereby the inner circumferentialsurface 41 f of the half bearing 41 comes into direct contact with thesurface of the journal part 6 and causes damage to the surface.

In contrast, as shown in the conventional technology of FIG. 16, if nooil hole is provided in one circumferential oil groove a (thecircumferential oil groove on the left in FIG. 16) out of the firstcircumferential oil groove a and a second circumferential oil groove bof the half bearing so that the lubricating oil does not flow from theoil distribution passage 81 b of the cylinder block 81 into the onecircumferential oil groove a, supply of the lubricating oil to thecrankpin part becomes insufficient and the crankpin part bearing islikely to be damaged while the inlet 6 b of the first lubricating oilpassage 6 a of the journal part 6 is in communication with the onecircumferential oil groove a.

In addition, by the time communication between the one circumferentialoil groove a and the inlet 6 b of the first lubricating oil passage 6 aof the journal part 6 is terminated, the amount of lubricating oil inthe one circumferential oil groove a has become small. Thus, immediatelyafter the termination of the communication, the lubricating oil aroundthe circumferential oil groove a is suctioned into the circumferentialoil groove a where the pressure has become relatively low. Therefore,due to insufficient amount of the lubricating oil, the innercircumferential surface surrounding the circumferential oil groove acomes into direct contact with the surface of the journal part, and thesurface of the journal part is likely to be damaged.

(Instantaneous Operation)

As described above, according to the conventional technology shown inFIG. 16, as soon as the inlet of the first lubricating oil passage ofthe journal part terminates the communication with the firstcircumferential oil groove, the amount of the lubricating oil inside thefirst circumferential oil groove near the circumferential end part canbe instantaneously insufficient.

In contrast, in the configuration where the first circumferential oilgroove 41 a and the second circumferential oil groove 41 b communicatewith each other through the inlet 6 b of the first lubricating oilpassage 6 a as shown in FIG. 6, the lubricating oil inside the firstlubricating oil passage 6 a and the lubricating oil inside the secondcircumferential oil groove 41 b flow to the first circumferential oilgroove 41 a, so that the amount of the lubricating oil does not becomeinsufficient.

More specifically, when the second circumferential oil groove 41 b andthe inlet 6 b of the first lubricating oil passage 6 a startcommunication with each other, the lubricating oil inside the oildistribution passage 81 b of the cylinder block 81 flows largely intothe second circumferential oil groove 41 b. The lubricating oil near theinlet 6 b is subjected simultaneously to the following operations: (1) acentrifugal force F1 due to rotation of the journal part 6, (2) a flowF2 due to the pressure gradient of the lubricating oil between theinside of the second circumferential oil groove 41 b and the inside ofthe first lubricating oil passage 6 a, and (3) a flow F3 due to thepressure gradient of the lubricating oil between the inside of the firstlubricating oil passage 6 a and the inside of the first circumferentialoil groove 41 a. Thus, in the lubricating oil having entered the firstlubricating oil passage 6 a, a flow is instantaneously formed whichmoves reversely into the first circumferential oil groove 41 a.

However, since the communication between the first circumferential oilgroove 41 a and the second circumferential oil groove 41 b is aninstantaneous phenomenon, it causes substantially no increase in theinternal volume of the oil groove. That is, it is not necessary to setthe amount of discharge oil of the oil pump to a larger amount on thebasis of the total internal volume of the first and secondcircumferential oil grooves 41 a and 41 b.

(Advantages)

Next, the advantages provided by the bearing device 1 of the presentinvention will be enumerated and described below.

(1) The bearing device 1 of this embodiment is characterized in that onehalf bearing 41 held in the holding bore 81 a of the cylinder block 81has the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b, the separation part 41 c, and the firstoil hole 41 d and the second oil hole 41 e, and wherein the cylinderblock 81 has the oil distribution passage 81 b formed so as to extendacross both the first oil hole 41 d and the second oil hole 41 e.

According to this configuration, a part of the lubricating oil issupplied to the second circumferential oil groove 41 b through the oildistribution passage 81 b and the second oil hole 41 e even when theinlet 6 b of the first lubricating oil passage 6 a of the journal part 6is in communication with the first circumferential oil groove 41 a. Forthis reason, it is unlikely that the amount of the lubricating oilbecomes insufficient on the inner circumferential surface 41 f near thesecond circumferential oil groove 41 b and the inner circumferentialsurface 41 f of the half bearing 41 comes into direct contact with thesurface of the journal part 6.

A large part of the lubricating oil is alternately fed to the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b. Thus, since the amount of the discharge oil of the oil pumpcan be set on the basis of the internal volume of one circumferentialoil groove 41 a (41 b), a sufficient amount of lubricating oil can besupplied even by a small oil pump. In addition, since the lubricatingoil is supplied to the first lubricating oil passage 6 a of the journalpart 6 through both the circumferential oil grooves 41 a and 41 b, thelubricating oil can be continuously supplied to the crankpin part 5.

(2) Since the length L1 in the circumferential direction of theseparation part 41 c at a position in the inner circumferential surfaceof the upper half bearing 41 is smaller than the length L2 in thecircumferential direction of the inlet 6 b of the journal part 6, thefirst circumferential oil groove 41 a and the second circumferential oilgroove 41 b can communicate with each other through the inlet 6 b of thejournal part 6. Thus, as the lubricating oil inside the firstlubricating oil passage 6 a and the lubricating oil inside the secondcircumferential oil groove 41 b flow into the first circumferential oilgroove 41 a, the amount of the lubricating oil does not becomeinsufficient.(3) The length L1 in the circumferential direction of the separationpart 41 c and the length L2 in the circumferential direction of theinlet 6 b of the journal part 6 satisfy the following relationalexpression: L1≧L2×0.5. Thus, the required amount of lubricating oil canbe supplied to the crankpin part 5 by limiting the area of the clearancebetween the separation part 41 c and the inlet 6 b. That is, if thelength L1 in the circumferential direction of the separation part 41 cis too short, the time during which the first circumferential oil groove41 a and the second circumferential oil groove 41 b communicate witheach other through the inlet 6 b of the journal part 6 becomes longer,and the amount (leak amount) of the lubricating oil flowing from the onecircumferential oil groove 41 b to the other circumferential oil groove41 a increases, resulting in a smaller amount of lubricating oil beingsupplied to the crankpin part 5.(4) It is possible to prevent leakage of the lubricating oil from onecircumferential oil groove to the other circumferential oil groove overthe separation part 41 c by making the length L1 in the circumferentialdirection of the separation part 41 c at a position in the innercircumferential surface of the half bearing 41 to be 1 mm or longer.That is, when the length L1 in the circumferential direction of theseparation part 41 c is shorter than 1 mm, the lubricating oil insidethe one circumferential oil groove flows easily into the othercircumferential oil groove over the separation part 41 c by beingentrained on the surface of the rotating journal part 6.(5) When the length in the circumferential direction of the separationpart 41 c at a position in the inner circumferential surface of theupper half bearing 41 is L1, and the length in the circumferentialdirection of the inlet 6 b of the journal part 6 is L2, the followingexpression L2-L1>0.5 (mm) is satisfied. Thus, the clearance having apredetermined area provided between the separation part 41 c and theinlet 6 b allows the lubricating oil inside the first lubricating oilpassage 6 a and the lubricating oil inside the second circumferentialoil groove 41 b to flow more easily to the first circumferential oilgroove 41 a.(6) The total internal volume obtained by adding up the internal volumeof the first circumferential oil groove 41 a and the internal volume ofthe second circumferential oil groove 41 b is smaller than the internalvolume of the oil distribution passage 81 b. Thus, in a state where thefirst circumferential oil groove 41 a and the second circumferential oilgroove 41 b communicate with each other through the inlet 6 b, theamount of lubricating oil which is instantaneously required can besecured inside the oil distribution passage 81 b. Thus, the amount oflubricating oil supplied to the circumferential oil grooves 41 a and 41b can be prevented from becoming instantaneously insufficient.

Embodiment 2

In the following, the bearing device 1 having the half bearing 41 of adifferent form from that of Embodiment 1 will be described withreference to FIG. 7. The parts that are the same as or equivalent tothose described in Embodiment 1 will be denoted by the same referencesigns.

(Configuration)

Similarly to Embodiment 1, the bearing device 1 of this embodimentincludes the journal part 6, the main bearing 4, the cylinder block 81,and the bearing cap 82. Among these parts, the half bearing 41 of thisembodiment has the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b each of which is deepest at a positionnear the center in the circumferential direction of the half bearing 41and gradually decreases in depth toward the end part. The firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b are open on the circumferential end surfaces 41 g, 41 g ofthe half bearing 41.

(Operational Advantages)

Thus, since the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b are deepest at a position near thecenter in the circumferential direction of the half bearing 41 andgradually decrease in depth toward the end parts, it is possible tointroduce the lubricating oil into the first circumferential oil groove41 a and the second circumferential oil groove 41 b without disturbingthe flow of the lubricating oil. In addition, it becomes easier toachieve the reduction in size of the oil pump by reducing the internalvolumes of the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b.

Description of other configurations and operational advantages, whichare almost the same as those of Embodiment 1, will be omitted here.

Embodiment 3

In the following, the bearing device 1 having the half bearing 41 of adifferent form from that of Embodiments 1 and 2 will be described withreference to FIG. 8. The parts that are the same as or equivalent tothose described in Embodiments 1 and 2 will be denoted by the samereference signs.

(Configuration)

Similarly to Embodiments 1 and 2, the bearing device 1 of thisembodiment includes the journal part 6, the main bearing 4, the cylinderblock 81, and the bearing cap 82. Among these parts, the half bearing 41of this embodiment has the first circumferential oil groove 41 a and thesecond circumferential oil groove 41 b which are respectively deepest ata position near the center in the circumferential direction of the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b and gradually decrease in depth toward the end parts.

Unlike Embodiment 1, the first circumferential oil groove 41 a and thesecond circumferential oil groove 41 b are not open on thecircumferential end surfaces 41 g, 41 g of the half bearing 41. In otherwords, the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b communicate with the inlet 6 b of theoil passage of the journal part 6 in most of the region in thecircumferential direction, but do not communicate with the inlet 6 b ofthe oil passage of the journal part 6 near the end parts.

(Operational Advantages)

Thus, since the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b are respectively deepest at a positionnear the center in the circumferential direction of the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b and gradually decrease in depth toward the end parts, it ispossible to introduce the lubricating oil into the first circumferentialoil groove 41 a and the second circumferential oil groove 41 b withoutdisturbing the flow of the lubricating oil. Moreover, as the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b are not open on the circumferential end surfaces 41 g, 41 g,no discontinuous connection portion is formed, so that the lubricatingoil can flow more smoothly. In addition, it becomes easier to achievethe reduction in size of the oil pump by reducing the internal volume ofthe first circumferential oil groove 41 a and the second circumferentialoil groove 41 b.

Description of other configurations and operational advantages, whichare almost the same as those of Embodiments 1 and 2, will be omittedhere.

Embodiment 4

In the following, the bearing device 1 having the half bearing 41 of adifferent form from that of Embodiments 1 to 3 will be described withreference to FIGS. 9 and 10. The parts that are the same as orequivalent to those described in Embodiments 1 to 3 will be denoted bythe same reference signs.

Similarly to Embodiments 1 and 2, the bearing device 1 of thisembodiment includes the journal part 6, the main bearing 4, the cylinderblock 81, and the bearing cap 82. Among these parts, the half bearing 41of this embodiment includes crash reliefs 41 h, 41 h at thecircumferential end parts on the inner circumferential surface side.

As shown in FIGS. 9 and 10, the crash relief 41 h is formed by thinningthe wall of the half bearing 41 in the radial direction, in the regionof the circumferential end part, from the original inner circumferentialsurface 41 f (sliding surface, major arc) which is concentric with therotational center.

The crash relief 41 h is formed for absorbing a positional shift ordeformation of the circumferential end surfaces 41 g, 41 g of the halfbearings 41 and 42, the positional shift or deformation being causedwhen the pair of half bearings 41 and 42 is mounted to the journal part6 of the crankshaft.

Thus, the position of center of curvature of the inner circumferentialsurface in the region where the crash relief 41 h is formed is differentfrom the position of center of curvature of the inner circumferentialsurface (sliding surface, major arc) in other regions (see SAE J506(item 3.26 and item 6.4), DIN 1497, section 3.2, and JIS D3102).Generally, in the case of the bearing for small internal combustionengines of passenger cars, the depth of the crash relief at thecircumferential end surface of the half bearing (distance from theoriginal inner circumferential surface to the actual innercircumferential surface) is approximately 0.01 to 0.05 mm.

The crash relief 41 h gradually decreases in depth toward the center inthe circumferential direction of the half bearing 41, and connects withthe inner circumferential surface 41 f at a predetermined connectionposition. As shown in FIGS. 9 and 10, the position at which the crashrelief 41 h connects with the inner circumferential surface 41 f may becloser to the center in the circumferential direction of the first andsecond circumferential oil grooves 41 a and 41 b than to thecircumferential end part. That is, the first and second circumferentialoil grooves 41 a and 41 b may be open on the crash reliefs 41 h, 41 h.Alternatively, the position at which the crash relief 41 h connects withthe inner circumferential surface 41 f may be closer to thecircumferential end part of the first and second circumferential oilgrooves 41 a and 41 b than to the center in the circumferentialdirection.

Description of other configurations and operational advantages, whichare almost the same as those of Embodiments 1 to 3, will be omittedhere.

While the embodiments of the present invention have been described abovein detail with reference to the drawings, the specific configurationsare not limited to these embodiments, and design changes to such adegree that does not depart from the scope of the present invention areincluded in the present invention.

For example, in the above embodiments, the first circumferential oilgroove 41 a and the second circumferential oil groove 41 b are equal ingroove width, groove depth, extent of formation, etc. However, thepresent invention is not limited to this example, and the firstcircumferential oil groove 41 a and the second circumferential oilgroove 41 b may be different in groove width, groove depth, extent offormation, etc. Nevertheless, the load on the oil pump can be leveled ifthe first circumferential oil groove 41 a and the second circumferentialoil groove 41 b are almost equal in internal volume, which makes iteasier to achieve the reduction in size of the oil pump.

Although it is not limited in the above embodiments, the separation part41 c is preferably formed so as to include the center position in thecircumferential direction of the half bearing 41. However, the centerposition of the length LI in the circumferential direction of theseparation part 41 c may also be shifted toward the circumferential endpart with respect to the center position in the circumferentialdirection of the half bearing 41.

Although the first oil hole 41 d and the second oil hole 41 e have acircular shape in the above embodiments, the present invention is notlimited to this example. For example, the first oil hole 41 d and thesecond oil hole 41 e may have an oval shape, an elongated hole shape(FIG. 15), or the like.

As have been described in Embodiments 2 and 3, the first circumferentialoil groove 41 a and the second circumferential oil groove 41 b may havea configuration where their circumferential end parts are open on thecircumferential end surfaces 41 g, 41 g of the half bearing 41, or aconfiguration where they are not open on the circumferential endsurfaces 41 g, 41 g. Another possible configuration is that only one ofthe first circumferential oil groove 41 a and the second circumferentialoil groove 41 b is open on the circumferential end surface 41 g whilethe other is not open on the circumferential end surface 41 g.

Although it is not limited in the above embodiments, the width dimensionof the first circumferential oil groove 41 a and the secondcircumferential oil groove 41 b is preferably smaller than the diameterof the inlet 6 b of the first lubricating oil passage 6 a of the journalpart 6.

Although in the above embodiments, the wall thickness of the halfbearings 41 and 42 in the region of the inner circumferential surface(sliding surface, major arc) is constant over the entire length in thecircumferential direction, the present invention is not limited to thisexample. For example, the wall thickness of the half bearings 41 and 42in the region of the inner circumferential surface (sliding surface,major arc) may gradually decrease or gradually increase from the centerin the circumferential direction of the half bearings 41 and 42 towardthe circumferential end parts.

1. A bearing device for rotatably supporting a journal part of acrankshaft, comprising: a journal part having an oil passage extendinginside thereof and an inlet of the oil passage being open on an outercircumferential surface of the journal part; a main bearing beingconstituted of a pair of half bearings and rotatably supporting thejournal part; and a cylinder block and a bearing cap being each formedwith a holding bore for holding the main bearing, wherein one halfbearing being held in the holding bore of the cylinder block includes: afirst circumferential oil groove and a second circumferential oil groovebeing formed at positions opposite to the inlet of the oil passage ofthe journal part in an inner circumferential surface of the one halfbearing; a separation part separating the first circumferential oilgroove and the second circumferential oil groove; and a first oil holeand a second oil hole respectively penetrating from the firstcircumferential oil groove and the second circumferential oil groove toan outer circumferential surface of the one half bearing, and thecylinder block includes an oil distribution passage being formed in aholding surface constituting the holding bore so as to extend acrossboth the first oil hole and the second oil hole of the one half bearing.2. The bearing device according to claim 1, wherein a length L1 in acircumferential direction of the separation part at a position in theinner circumferential surface of the one half bearing is smaller than alength L2 in the circumferential direction of the inlet of the journalpart.
 3. The bearing device according to claim 1, wherein a followingexpression is satisfied:L1≧L2×0.5 where L1 is the length in the circumferential direction of theseparation part at a position in the inner circumferential surface ofthe one half bearing, and L2 is the length in the circumferentialdirection of the inlet of the journal part.
 4. The bearing deviceaccording to claim 1, wherein the length L1 in the circumferentialdirection of the separation part at a position in the innercircumferential surface of the one half bearing is 1 mm or longer. 5.The bearing device according to claim 1, wherein a following expressionis satisfied:L2−L1>0.5 (mm) where L1 is the length in the circumferential directionof the separation part at a position in the inner circumferentialsurface of the one half bearing, and L2 is the length in thecircumferential direction of the inlet of the journal part.
 6. Thebearing device according to claim 1, wherein a total internal volumeobtained by adding up an internal volume of the first circumferentialoil groove and an internal volume of the second circumferential oilgroove is smaller than an internal volume of the oil distributionpassage.